1. Field of the Invention
The present invention relates to a scroll compressor for use as a refrigerant compressor for refrigerator, air conditioner or an air compressor, etc. and, particularly, more an arrangement for decreasing the weight and adjustment of balance of an orbiting scroll of a scroll compressor in order to assure the operation of the compressor at a high speed.
2. Description of the Prior Art
In conventional scroll compressors comprise a housing having a suction tube and a discharge tube, a frame fixedly mounted in the housing, a fixed scroll fixedly connected to the with frame and having an end plate, a spiral wrap upstanding from the end plate in the form of an involute or a nearly involute shape, and with a discharge port formed near the center of said end plate and a suction port formed at the peripheral portion of said end plate. An orbiting scroll is arranged in the frame for a revolving movement, with the orbiting scroll having an end plate and a spiral wrap upstanding from the end plate in the form of an involute or a nearly involute shape. The orbiting scroll and the fixed scroll are so arranged that their wraps are directed inward so as to mesh with each other.
A rotation inhibiting mechanism, such as Oldham mechanism, is arranged between the orbiting scroll and the frame to prevent the orbiting scroll from rotating about its own axis. A bearing boss is formed on the back surface of the end plate of the orbiting scroll. A drive shaft, driven by a motor, has an eccentric shaft portion which is held in engagement with the bearing boss.
By a revolving motion of the eccentric shaft portion, the orbiting scroll produces an orbiting motion, without producing rotation thereof about its own axis. Thus, a gas contained in a confined space formed by the orbiting scroll and the fixed scroll is successively compressed and the compressed gas is discharged from the discharge port.
Heretofore, the fixed scroll and the orbiting scroll have been made of cast iron, which has a relatively heavy weight. Accordingly, when the orbiting scroll is rotated at a high speed, the load on the bearing is increased to a centrifugal force acting on the orbiting scroll, thereby resulting in a lowering of the reliability of the compressor.
In order to enable the operation of the scroll compressor at higher speed, it has been proposed to decrease the weight of the orbiting scroll by making the orbiting scroll of a material having a low specific weight, such as aluminum alloy. Furthermore, it has been proposed to provide a construction in which asymmetrically arranged recesses are formed in the end plate of the orbiting scroll in order to locate the center of gravity of the orbiting scroll in alignment with the central axis of the bearing bass. Such a construction is shown in, for example Japanese Patent Application Laid-Open No. Sho 58-110886.
Furthermore, in order to prevent the increase of the load applied to the compressor due to compression of a fluid, such as a lubricating oil, which passes through the gap between the peripheral portion of the end plate of the orbiting scroll and the frame during a revolving of the orbiting scroll, it has been proposed to provide a construction in which grooves are formed in the surface of the frame adjacent to the peripheral portion of the end plate or small grooves are formed in a part of the peripheral portion of the end plate, whereby the fluid can easily pass through the gap. An example of such construction is shown in, for example Japanese Patent Application Laid-Open No. Sho 59-119091.
According to the prior art described above, if the orbiting scroll is made of a cast iron, which has a heavy weight, the load on the bearing owing to the centrifugal force of the orbiting scroll during operation at a high speed is increased, with the result that the reliability of the compressor is lowered. On the other hand, if the orbiting scroll is made of a metallic material having a low specific weight, such as aluminum alloy, it is necessary to provide relatively wide gaps at the tip ends of the wraps of fixed scroll and the orbiting scroll, since the fixed scroll and the frame made of cast iron and the orbiting scroll made of aluminum alloy have substantial difference in coefficient of thermal expansion, etc. Therefore, it is necessary to provide tip seals at the tip ends of the wraps in order to seal the confined compressing space.
In the construction heretofore proposed in which means are provided to locate the center of gravity of the orbiting scroll in alignment with the central axis of the bearing boss, such as shown in Japanese Patent Application No. Sho 58-110886 etc., no consideration is given to decreasing the weight of the orbiting scroll, which is necessary to operate the compressor at a high speed.
In the construction as shown in Japanese Patent Application Laid-Open No. Sho 59-119091, means are provided to prevent the increase of the load due to the compression of the fluid at the peripheral portion of the end plate of the orbiting scroll. However, no consideration is given to decreasing the weight of the orbiting scroll and locating the center of gravity of the orbiting scroll in substantial alignment with the central axis of the bearing boss, which is necessary to assure high speed operation of the compressor.